This disclosure generally relates to turbine systems, and more particularly to environmentally resistant coatings for the various components employed in such turbine systems.
Turbines are devices that generate rotary mechanical power from the energy in a stream of moving-fluid, and may be used in aircraft, watercraft (both marine and fresh water), various types of landcraft, and the like. Materials from which turbine components may be fabricated typically include those from a class of materials known as superalloys, particularly superalloys in which the base constituent is an alloy of nickel (Ni), iron (Fe), or cobalt (Co). Despite their generally superior chemical and physical properties, temperature constraints, particularly for single-crystal nickel-based superalloys, can limit the use of such superalloys in turbine engines in which extreme temperature conditions may be experienced.
In order to overcome some of the temperature limitations of these superalloys, newer materials based on niobium (Nb) and molybdenum have been developed. The niobium based materials used in turbine applications are termed niobium based refractory metallic-intermetallic composites (hereinafter Nb based RMICs), while those based on molybdenum are termed molybdenum-silicide based composites. Both Nb based RMICs and molybdenum-silicide based composites have melting temperatures greater than 1700xc2x0 C., which exceeds the current temperature service limit of nickel based superalloys.
Although the Nb based RMICs and molybdenum-silicide based composites display high melting temperatures, they can undergo rapid oxidation at temperatures of about 1090xc2x0 C. to about 1370xc2x0 C. In addition, another type of oxidation, generally termed as xe2x80x98pestingxe2x80x99, occurs at intermediate temperatures of about 760xc2x0 C. to about 990xc2x0 C. Pesting is a phenomenon that is characterized by the disintegration of a material into pieces or powders after exposure to air at intermediate temperatures. Refractory metals, particularly molybdenum, exhibit poor resistance to pesting oxidation. It is therefore desirable to be able to manufacture turbine components that are capable of withstanding service temperatures of greater than or equal to about 1000xc2x0 C., that have an increased resistance to oxidation at temperatures of about 1090xc2x0 C. to about 1370xc2x0 C., and that have an increased resistance to pesting at temperatures of about 760xc2x0 C. to about 980xc2x0 C.
A turbine component comprises a substrate; and a crystalline coating disposed on a surface of the substrate, wherein the crystalline coating comprises tin and yttrium in an amount greater than or equal to about 0.05 atomic percent based upon the total coating.
In one embodiment, a method of making a turbine component comprises disposing a coating composition on a substrate, wherein the coating composition comprises tin and yttrium in an amount greater than or equal to about 0.1 atomic percent based upon the total coating composition.
In another embodiment, a crystalline coating comprises tin and yttrium in an amount greater than or equal to about 0.05 atomic percent based upon the total coating.
The above described and other features are exemplified by the following figures and the detailed description.